You can pick out quite a few potential trouble spots for the Toronto Maple Leafs, even just on the basis of six preseason games.

The recent run of injuries, and the daily Tim Connolly Health Watch™, raise one potential issue – even if that's something that can affect any team, at any time.

An ugly sophomore slump from James Reimer may be another.

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What doesn't appear to be a problem, however, will be the effort level from the Leafs best line of a year ago, as Mikhail Grabovski and Co. have been their regular old selves in training camp as preseason winds down.

Ron Wilson even remarked the other day how the team's new assistant coaches were pretty impressed with the three – and their centre, in particular.

"I've gotten kind of used to him," Wilson said of Grabovski. "Then you have two new coaches come in, they haven't seen him play much, and they're like 'ooo, this guy's a really good hockey player.' And the kind of player that coaches appreciate because he's got detail in his game."

Some of those details aren't always readily apparent from simply watching their games. One aspect of his game that Grabovski and his linemates all have is a terrific "after hours" work ethic, as they watch more video than anyone else on the team and often do so together.

Grabovski and Nikolai Kulemin are also often on the coaches' whiteboard on the ice during practice, drawing up plays or talking with a coach about what this or that system means. (The new clog-the-neutral-zone penalty kill has offered some of those opportunities already.)

Scott Gordon, one of Wilson's new assistants, noted this week he hasn't really seen that sort of connection before in NHL linemates.

"As I'm learning here, both [Kulemin]and Grabo, they're students of the game," Gordon said. "They constantly work on their game. Trying to understand it.

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"Ron put it best to me, with Grabo, he doesn't just want to be told, he wants to understand what the reasoning is. Some guys don't think twice about it, they just go and do it. But both those guys, they want to get better and want to understand why we do what we do.

"I don't think you'll find three players, as a line, that'll talk more about their shifts ... That's something they do very well. They get together and understand where each guy's coming from. I think lines talk in general but to actual sit down and watch video? And go into a corner and have lengthy discussions about it? That's the exception to the rule."

Their teammates all pick up on that unique connection, too. The Connolly line has been asked plenty during camp about generating chemistry together, and Joffrey Lupul commented that maybe they should take after the Grabovski line and hold video sessions together.

"If we have to do that, I'm all for it," he said.

It may have been a preseason game, against the rebuilding Ottawa Senators, but Tuesday's win spurred a lot of talk about these three this week in Toronto. Grabovski looked like a man possessed, with a goal and two assists, which is an odd state of mind for a veteran player in a meaningless exhibition game.

Why he felt as though he had to return to the game after taking a big bump from Chris Neil, we'll never know, but he earned kudos from Wilson afterwards when he named him his team's "toughest player."

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All that said, anytime you bring up these three as being the Leafs first line, there are definitely eye rolls across the country. Few believe they're worthy of the designation or can repeat their 80-goal performance of a year ago, one that put them ahead of some pretty solid team's top three forwards.

(As I wrote earlier, the Leafs top four forwards actually scored a remarkable number of goals compared the top teams in the Eastern Conference, and that's a group that includes all three of Grabovski, Kulemin and MacArthur.)

"Question: Is Grabovski's line a first line in the NHL?" Sportsnet's Mark Spector asked on Twitter recently. "Or just a first line on a non-playoff team?"

The answer to the first question at this point is a definite "yes," if only because they've been the Leafs best line since the 2010 training camp started a year ago.

The second question?

Well, that depends. Can all three repeat career years? Can all three stay healthy? Will Wilson keep them together if other lines struggle?

And, most of all, can the Leafs overcome all those "trouble spots" mentioned earlier that will help get out of the "non-playoff team" designation?

That goes beyond Grabovski, Kulemin and MacArthur, obviously, but they're going to be a huge part of whatever success the Leafs have. They scored nearly 40 per cent of Toronto's goals a year ago and may have to again, especially given Wilson has said he could shift to them as his top power play unit.

Other teams will also key in on them more, just as they did late last season with their top checkers.

But their effectiveness goes beyond simply goal production, as Grabovski and Kulemin will likely be key penalty killers, and in some of the advanced stats mentioned here, all three were among the league leaders a year ago.

Add all that up, and the reality is that, while Dion Phaneuf and Phil Kessel get much of the media attention, Grabovski and Kulemin are this team's top players. And MacArthur's not that far behind.

Along with James Reimer, they need as big a follow-up year as anyone on this team in order for the Leafs to surprise and sneak into eighth place.

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